Multilayer ceramic capacitor and process for producing the same

ABSTRACT

A multilayer ceramic capacitor and a process for producing the same, which comprises dielectric ceramic layers, internal electrodes disposed between the dielectric ceramic layers, and an external electrode connected to the internal electrodes, the dielectric ceramic layers comprising barium titanate, a bismuth compound, and an anti-reducing agent, the internal electrodes comprising nickel or a nickel alloy.

This is a continuation of application Ser. No. 08/622,068, filed Mar.26, 1996, now U.S. Pat. No. 5,853,515, which was a division ofapplication Ser. No. 08/478,026, filed Jun. 7, 1995 and now U.S. Pat.No. 5,600,533.

FIELD OF THE INVENTION

The present invention relates to a multilayer ceramic capacitor and aprocess for producing the same.

BACKGROUND OF THE INVENTION

A multilayer ceramic capacitor comprises dielectric ceramic layers,internal electrodes disposed between the dielectric ceramic layers, andan external electrode connected to these internal electrodes on bothsides of the dielectric ceramic layers.

Ceramic compositions having a high dielectric constant comprising bariumtitanate as a major component have conventionally been used as amaterial for dielectric ceramic layers. In particular, a compositioncomprising barium titanate as a major component and, incorporatedtherein as a minor component, a bismuth compound, such as the titanate,stannate, and zirconate of bismuth oxide, has been widely employed fromthe standpoint of diminishing fluctuations of dielectric constant withtemperature and voltage. The conventional dielectric ceramic layers havebeen formed by firing such a dielectric material at temperatures around1,200° C.

Because of such high temperatures used for the firing of dielectricmaterials, substances having a high melting point and less susceptibleto oxidation at high temperatures, e.g., a silver-palladium alloy andplatinum, have been used as a material for internal electrodes. Afterthe formation of dielectric ceramic layers and internal electrodes,external electrodes have been formed by baking silver, etc.

However, the use of noble metals such as platinum and silver-palladiumalloys as internal electrodes has been a serious obstacle to costreduction in multilayer ceramic capacitors, since these materials areexpensive. Another problem is that the internal electrodes made of asilver-palladium alloy may suffer deterioration in properties due tosilver migration. Furthermore, the internal electrodes made of platinumhave a drawback that the electrodes have an increased equivalent seriesresistance because of the low electrical conductivity of platinum.

It has been proposed that a base metal having a high melting point, suchas nickel, cobalt, and tungsten, may be used for overcoming theabove-described problems. However, these base metals are so readilyoxidized in a high-temperature oxidizing atmosphere that they do notfunction as an electrode. Therefore, for using these base materials asthe internal electrodes of multilayer ceramic capacitors, it isnecessary that they must be fired in a neutral or reducing atmospherealong with a dielectric material.

However, if the dielectric material described above comprising bariumtitanate as a major component and a bismuth compound as a minorcomponent is fired in a neutral or reducing atmosphere, the bariumtitanate and bismuth oxide contained in the dielectric material arereduced and this results in a problem in that the dielectric ceramiclayers thus obtained have a reduced insulation resistance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an inexpensivemultilayer ceramic capacitor free from any property deterioration causedduring production.

Another object of the present invention is to provide a process forproducing the multilayer ceramic capacitor.

Other objects and effects of the present invention will be apparent fromthe following description and examples.

The present invention relates to a multilayer ceramic capacitorcomprising dielectric ceramic layers, internal electrodes disposedbetween the dielectric ceramic layers, and an external electrodeconnected to the internal electrodes,

the dielectric ceramic layers comprising barium titanate, a bismuthcompound, and an anti-reducing agent,

the internal electrodes comprising nickel or a nickel alloy.

The present invention also relates to a process for producing amultilayer ceramic capacitor which comprises the steps of:

forming, by a thin-film forming method, a nickel or nickel alloy layeron ceramic green sheets comprising barium titanate, a bismuth compound,and an anti-reducing agent;

superposing the ceramic green sheets on one another to form anassemblage; and

subjecting the assemblage to high-speed firing.

In the multilayer ceramic capacitor and the process for producing thesame according to the present invention, the anti-reducing agent ispreferably represented by general formula:

    αMOx+βRO+γB.sub.2 O.sub.3 +(100-α-β-γ)SiO.sub.2

wherein MOx represents one member selected from the group consisting ofMnO₂, Li₂ O, and ZnO; R represents at least one member selected from thegroup consisting of Mg, Sr, Ca, and Ba; and α, β, and γ, each indicatingpercentage by mole, represent numbers of 5≦α≦20, 10≦β≦60, and 20≦γ≦35,respectively.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of one embodiment of the multilayer ceramiccapacitor according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The dielectric material used for the dielectric ceramic layer in thepresent invention is not particularly limited. Examples of thedielectric material include compositions containing barium titanate as amajor component and a bismuth compound as a minor component, such asaBaTiO₃ +bBi₂ O₃ +cTiO₂ +dM+ePb₃ O₄ +fNb₂ O₅ (wherein M is one memberselected from La₂ O₃, CeO₂, Nd₂ O₃, Sm₂ O₃, and Y₂ O₃, and a, b, c, d,e, and f each is a constant);

BaTiO₃ +Bi₂ O₃.SnO₂ +Nd₂ O₃ ;

BaTiO₃ +Bi₂ O₃.SnO₂ +CaZrO₃ +MgTiO₃ +CeO₂ ; and

BaTiO₃ +Bi₂ O₃.ZrO₂ +CeO₂.

The composition of the dielectric material is not particularly limited.The content of barium titanate is generally 70 wt % or more, preferably80 wt % or more; and the content of the bismuth compound is generally 30wt % or less, preferably 20 wt % or less, all based on the total amountof barium titanate and the bismuth compound. The content of Bi₂ O₃ asthe bismuth compound is generally 15 wt % or less, preferably 10 wt % orless, based on the total amount of barium titanate and the bismuthcompound.

The dielectric material is mixed with the anti-reducing agent. Theproportions of the dielectric material and the anti-reducing agent arenot particularly limited, and the content of the dielectric material isgenerally 70 wt % or more, preferably from 80 to 99 wt %; and thecontent of the anti-reducing agent is generally 30 wt % or less,preferably from 1 to 20 wt %, all based on the total amount of thedielectric material and the anti-reducing agent.

The ceramic green sheet can be prepared by using the dielectric materialand the anti-reducing agent along with an organic binder and a solvent.The organic binder and the solvent, as well as a method for forming thegreen sheet, are not particluarly limited and each may be anyconventional one.

Although nickel or a nickel alloy is used as the metal film serving asan internal electrode, it is also possible to form an internal electrodeconsisting of two or more metal films, in which a film of copper to bealloyed with nickel was first deposited and a nickel metal film was thendeposited thereon. In this case, electrical conductivity, melting point,and susceptibility to oxidation may vary depending on the kind andthickness of the metal film used in combination with nickel. Hence, thekind and thickness of the metal film used in combination with nickel canbe appropriately determined from the compositions of the dielectricpowder and anti-reducing agent and the use of the multilayer ceramiccapacitor to be obtained.

The external electrode is not particularly limited and may be made of asuitable material such as, e.g., the same material as the internalelectrodes, silver, palladium, or a silver-palladium alloy. For formingthe external electrode, any known method, such as paste baking, vapordeposition, sputtering, plating, etc., can be employed.

The thin-film forming method used for forming a nickel or nickel alloylayer on ceramic green sheets preferably comprises the steps of:

forming a metal layer consisting of nickel or a nickel alloy on a resinfilm by a thin-film forming method;

patterning the metal layer into a form of an internal electrode byphotoetching;

superposing the resin film carrying the patterned metal layer on theceramic green sheet with the metal layer being sandwiched therebetween;and

pressing the resin film and the ceramic green sheet with heating tothereby transfer the metal film to the ceramic green sheet.

As the thin-film forming method used in the present invention, at leastone of a vapor deposition method, a sputtering method, and a platingmethod can be employed.

The material containing an anti-reducing agent, used for formingdielectric ceramic layers, can be fired in a neutral or reducingatmosphere having a partial oxygen pressure of from 10⁻⁶ to 10⁻¹⁰ MPa at1,000° C. to 1,200° C., without deteriorating the properties thereof.

Copper is known as a metal which can be sintered in a neutral atmospherehaving a partial oxygen pressure of about 10⁻⁷ MPa at around 1,000° C.However, copper is susceptible to oxidation even at relatively lowtemperatures. Hence, use of copper as a material for internal electrodesin the production of a multilayer ceramic capacitor has a drawback thatif firing is conducted in an atmosphere having a partial oxygen pressurehigher than the equilibrium partial oxygen pressure of Cu/CuO, diffusionof copper into the dielectric ceramic layers occurs during the firing,resulting in deteriorated properties. It is therefore necessary toprecisely control the atmosphere for firing.

In contrast, nickel is less apt to undergo oxidation reaction. Use ofnickel as internal electrodes is hence advantageous in that even wherefiring is conducted in an atmosphere having a partial oxygen pressurehigher than the equilibrium partial oxygen pressure of Ni/NiO, themultilayer ceramic capacitor thus produced is less apt to sufferproperty deterioration if the firing used is high-speed short-timefiring. Thus, the high-speed firing is preferably used in the presentinvention. In the high-speed firing, the temperature increasing(heating) and decreasing (cooling) rates are generally 6° C./min ormore, preferably 8° C./min or more.

In particular, in the case where internal electrodes of either nickel ora nickel alloy are formed from metal films made by a thin-film formingmethod such as, e.g., vapor deposition, sputtering, or plating, themultilayer ceramic capacitor obtained is free from propertydeterioration even when the firing atmosphere used is a neutral orreducing atmosphere having a partial oxygen pressure of from 10⁻⁶ to10⁻¹⁰ MPa at 1,000° C. to 1,200° C.

As apparent from the above description, according to the presentinvention, the dielectric ceramic layers are prevented from beingreduced during firing to lower the insulation resistance of the ceramic,due to the function of the anti-reducing agent. Further, since internalelectrodes are formed using nickel or a nickel alloy preferably throughhigh-speed firing, the internal electrodes are prevented from beingoxidized to cause the ceramic to have an increased dielectric loss and areduced dielectric constant.

Moreover, since nickel or a nickel alloy is used as the material ofinternal electrodes, property deterioration caused by migration of aninternal-electrode component can be prevented.

The use of nickel or a nickel alloy, which are less expensive thanconventionally employed noble metals, as internal electrodes and theemployment of high-speed firing are also effective in attaining a costreduction.

Consequently, an inexpensive multilayer ceramic capacitor free fromproperty deterioration caused during production can be obtainedaccording to the present invention.

FIG. 1 is a sectional view of one embodiment of the multilayer ceramiccapacitors obtained in the following Examples. In the FIGURE, numeral 1denotes a dielectric ceramic layer containing barium titanate as a majorcomponent and a bismuth compound and an anti-reducing agent as minorcomponents. Numeral 2 denotes an internal electrode comprising nickel ora nickel alloy, and 3 denotes an external electrode.

The present invention is then explained in more detail by means ofExamples but should not be construed as being limited thereto.

EXAMPLE 1

BaTiO₃, Bi₂ O₃, TiO₂, CeO₂, Pb₃ O₄, and Nb₂ O₅ were prepared as startingmaterials for a dielectric powder.

The BaTiO₃ was obtained from high-purity TiCl₄ and Ba(NO₃)₂ in an amountratio of 1.000 in terms of the molar ratio of Ba ions to Ti ions. Thesecompounds were subjected to precipitation with oxalic acid to yield aprecipitate of barium titanyl oxalate (BaTiO(C₂ O₄).4H₂ O). Theprecipitate was pyrolyzed at a temperature of 1,050° C. to synthesizethe desired compound, which was then ground with a dry pulverizer untilthe average particle diameter thereof had decreased to 1 μm or smaller.

These materials were weighed out so as to yield a dielectric representedby 84.4BaTiO₃ +6.8Bi₂ O₃ +1.9TiO₂ +0.8CeO₂ +4.2Pb₃ O₄ +1.9Nb₂ O₅ (wt %),and then wet-ground and mixed in a ball mill for 16 hours to obtain adielectric powder having a particle diameter of 1 μm or smaller.

For obtaining anti-reducing agents represented by αLi₂ O+βRO+γB₂ O₃+(100-α-β-γ)SiO₂ (wherein R is at least one member selected from Mg, Sr,Ca, and Ba, and α, β, and γ indicate percentage by mole), the necessaryraw materials in the form of an oxide, carbonate, or hydroxide wereweighed out so as to yield anti-reducing agents having the compositionsshown in Table 1. These raw materials were wet-ground and mixed in aball mill to obtain powders. Each powder mixture was placed in analumina crucible, melted by heating to 1,300° C., kept molten for 1hour, and then quenched to vitrify the contents. These vitrifiedmixtures were pulverized to obtain anti-reducing agents each having anaverage particle diameter of 1 μm.

The dielectric powder and each anti-reducing agent obtained above weremixed in the proportion shown in Table 1. Thereto were added apoly(vinyl butyral) binder, ethanol, and toluene. This mixture wastreated with a ball mill for 16 hours to obtain a slurry, and thenformed into sheets by the doctor blade method. Thus, ceramic greensheets were obtained.

Separately, a nickel metal film having a thickness of 1.0 μm was formedon a poly(ethylene terephthalate) film by vapor deposition. This nickelmetal film was coated with a photoresist, which was then patterned intothe form of an internal electrode by the photoetching method.

This poly(ethylene terephthalate) film was placed on each of the ceramicgreen sheets in such a manner that the nickel metal film was in contactwith the ceramic green sheet. Using a hot press, the nickel metal filmwas then transferred to the ceramic green sheet. The ceramic greensheets to each of which the metal film had been transferred weresuperposed on one another to obtain an assemblage.

The assemblage was heated to 300° C. in air to burn out the organicbinder, and then subjected to high-speed firing in an atmospherecomposed of H₂, N₂, and H₂ O gases and having a partial oxygen pressureof from 10⁻⁶ to 10⁻¹⁰ MPa at the temperature shown in Table 1. Thefiring was performed under such conditions that the assemblage was firstheated to the maximum temperature at a rate of from 10° C./min to 17°C./min, subsequently maintained at that temperature for 30 to 60minutes, and then cooled to room temperature at a rate of from 8° C./minto 17° C./min.

A silver paste was applied to both sides of each of the thus-obtainedsinters, and the coating was baked in a nitrogen atmosphere at 600° C.to form an external electrode electrically connected to the internalelectrodes.

Thus, multilayer ceramic capacitors were obtained which had externaldimensions of 0.8 mm wide, 1.6 mm long, and 0.8 mm thick, and in whichthe thickness of each dielectric ceramic layer between internalelectrodes was 15 μm, the total number of effective dielectric ceramiclayers was 20, and the counter electrode area per layer was 0.45 mm².

The electrostatic capacity (C) and dielectric loss (tan δ) of each ofthe multilayer ceramic capacitors were measured at a temperature of 25°C. under conditions of a frequency of 1 kHz and 1 Vrms. From theelectrostatic capacity value obtained, the dielectric constant (ε) wascalculated. Further, a direct current voltage of 25 V was applied for 2minutes to measure the insulation resistance (R), and the product of theelectrostatic capacity (C) and the insulation resistance, i.e., CRproduct, was determined. The results obtained are shown in Table 1.

As comparative samples, the following capacitor samples were produced: Adielectric powder having the same composition as in the above, i.e.,represented by 84.4BaTiO₃ +6.8Bi₂ O₃ +1.9TiO₂ +0.8CeO₂ +4.2Pb₃ O₄+1.9Nb₂ O₅ (wt %), was used without the incorporation of ananti-reducing agent, to produce a multilayer ceramic capacitor (SampleNo. 1-10). A low-temperature sintering agent represented by 27.9Li₂O+7.4BaO+5.6CaO+5.6SrO+44.5SiO₂ +2.0TiO₂ +7.0CuO (mol. %) was added tothe same dielectric powder to produce a multilayer ceramic capacitor(Sample No. 1-11).

These comparative samples were evaluated for electric properties in thesame manner as above. The results obtained are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________             Anti-                     Firing                                        Dielectric reducing Composition of tempera-                                  Sample powder agent anti-reducing agent (mol %) ture                        No. (wt %)                                                                             (wt %)                                                                             Li.sub.2 O                                                                       BaO                                                                              CaO                                                                              SrO                                                                              MgO                                                                              B.sub.2 O.sub.3                                                                  SiO.sub.2                                                                        (° C.)                              __________________________________________________________________________      1-1 98 2 6 54  0  0 0 20 20 1,080                                             1-2 98 2 5  5  5  5 5 25 50 1,100                                             1-3 98 2 5 10 10  5 5 35 30 1,100                                             1-4 98 2 6  0 10  0 0 34 50 1,040                                             1-5 98 2 20   5  5  5 5 30 30 1,040                                           1-6 98 2 5 15 15 10 5 20 30 1,080                                             1-7 96 4 5 15 15 10 5 20 30 1,020                                             1-8 90 10  5 15 15 10 5 20 30   960                                           1-9 80 20  5 15 15 10 5 20 30   920                                           1-10* 100  0 -- -- -- -- -- -- -- 1,180                                       1-11* 96  4** -- -- -- -- -- -- -- 1,060                                    __________________________________________________________________________    Electric properties                                                           Sample No.                                                                          Dielectric constant ε                                                             Dielectric loss tan δ (%)                                                          CR product (Ω · F)                __________________________________________________________________________      1-1 2,120 2.0 4,100                                                           1-2 2,090 2.2 3,400                                                           1-3 1,950 2.1 4,000                                                           1-4 2.050 2.4 3,500                                                           1-5 1,900 2.0 4,300                                                           1-6 1,930 2.4 3,700                                                           1-7 1,780 1.9 3,100                                                           1-8 1,320 1.8 2,700                                                           1-9 1,050 2.3 2,100                                                         1-10* (unable to be measured)                                                 1-11* 1,550       10.8         200                                            __________________________________________________________________________     Note:                                                                         *Comparative sample                                                           **Lowtemperature sintering agent                                         

EXAMPLE 2

BaTiO₃, Bi₂ O³, ZrO₂, and CeO₂ were prepared as starting materials for adielectric powder. The BaTiO₃ used was the same as in Example 1.

These materials were weighed out so as to yield a dielectric representedby 93.6BaTiO₃ +3.3Bi₂ O₃ +2.6ZrO₂ +0.5CeO₂ (wt %), and then wet-groundand mixed in a ball mill for 16 hours to obtain a dielectric powderhaving a particle diameter of 1 μm or smaller.

Anti-reducing agents represented by αMnO₂ +βRO+γB₂ O₃ +(100-α-β-γ)SiO₂(wherein R is at least one member selected from Mg, Sr, Ca, and Ba, andα, β, and γ indicate percentage by mole) and having the compositionsshown in Table 2 were produced in the same manner as in Example 1.

Each of these anti-reducing agents was added to the dielectric powder inthe proportion shown in Table 2. Multilayer ceramic capacitors were thenproduced in the same manner as in Example 1.

Electric properties of these multilayer ceramic capacitors were measuredin the same manner as in Example 1. The results obtained are shown inTable 2.

Separately, a nickel powder paste having a particle diameter of 0.5 μmwas applied by screen printing to the same dielectric ceramic greensheets as in Sample No. 2-3 to form internal electrodes. These ceramicgreen sheets were superposed, and the resulting assemblage was treatedin the same manner as in Example 1 to produce a multilayer ceramiccapacitor (Sample No. 2-10).

                                      TABLE 2                                     __________________________________________________________________________             Anti-                     Firing                                        Dielectric reducing Composition of tempera-                                  Sample powder agent anti-reducing agent (mol %) ture                        No. (wt %)                                                                             (wt %)                                                                             Li.sub.2 O                                                                       BaO                                                                              CaO                                                                              SrO                                                                              MgO                                                                              B.sub.2 O.sub.3                                                                  SiO.sub.2                                                                        (° C.)                              __________________________________________________________________________      2-1 98 2 6 54  0  0 0 20 20 1,180                                             2-2 98 2 5  5  5  5 5 25 50 1,200                                             2-3 98 2 5 10 10  5 5 35 30 1,180                                             2-4 98 2 6  0 10  0 0 34 50 1,160                                             2-5 98 2 20   5  5  5 5 30 30 1,160                                           2-6 98 2 5 15 15 10 5 20 30 1,180                                             2-7 96 4 5 15 15 10 5 20 30 1,120                                             2-8 90 10  5 15 15 10 5 20 30 1,100                                           2-9 80 20  5 15 15 10 5 20 30 1,060                                           2-10 98 2 5 10 10  5 5 35 30 1,160                                          __________________________________________________________________________    Electric properties                                                           Sample No.                                                                          Dielectric constant ε                                                             Dielectric loss tan δ (%)                                                          CR product (Ω · F)                __________________________________________________________________________      2-1 2,730 2.3 3,900                                                           2-2 2,850 2.4 4,400                                                           2-3 2,650 2.4 4,100                                                           2-4 2,590 2.2 3,100                                                           2-5 2,520 2.2 3,500                                                           2-6 2,360 2.1 3,200                                                           2-7 2,110 2.2 3,100                                                           2-8 1,830 1.9 2,800                                                           2-9 1,340 2.5 2,000                                                           2-10   200 15.2  1,100                                                      __________________________________________________________________________

EXAMPLE 3

A dielectric powder represented by 93.6BaTiO₃ +3.3Bi₂ O₃ +2.6ZrO₂+0.5CeO₂ (wt %) and having a particle diameter of 1 μm or smaller wasobtained in the same manner as in Example 2.

Anti-reducing agents represented by αZnO₂ +βRO+γB₂ O₃ +(100-α-β-γ)SiO₂(wherein R is at least one member selected from Mg, Sr, Ca, and Ba, andα, β, and γ indicate percentage by mole) and having the compositionsshown in Table 3 were produced in the same manner as in Example 1.

Each of these anti-reducing agents was added to the dielectric powder inthe proportion shown in Table 3. Multilayer ceramic capacitors were thenproduced in the same manner as in Example 1.

Electric properties of these multilayer ceramic capacitors were measuredin the same manner as in Example 1. The results obtained are shown inTable 3.

Separately, the same assemblage as for Sample No. 3-3 was heated to 300°C. in air to burn out the organic binder, and then fired at 1,200° C. inan atmosphere composed of H₂, N₂, and H₂ O gases and having a partialoxygen pressure of from 10⁻⁶ to 10⁻¹⁰ MPa. The firing was performedunder such conditions that the assemblage was first heated to 1,200° C.at a rate of 3.0° C./min, subsequently maintained at that temperaturefor 2 hours, and then cooled to room temperature at a rate of 2.0°C./min.

The subsequent procedure was carried out in the same manner as inExample 1 to complete a multilayer ceramic capacitor.

An external electrode was then formed on the thus-obtained sinter in thesame manner as in Example 1 to fabricate a multilayer ceramic capacitor(Sample No. 3-10).

Electric properties of this multilayer ceramic capacitor were measuredin the same manner as in Example 1. The results obtained are shown inTable 3.

                                      TABLE 3                                     __________________________________________________________________________             Anti-                     Firing                                        Dielectric reducing Composition of tempera-                                  Sample powder agent anti-reducing agent (mol %) ture                        No. (wt %)                                                                             (wt %)                                                                             Li.sub.2 O                                                                       BaO                                                                              CaO                                                                              SrO                                                                              MgO                                                                              B.sub.2 O.sub.3                                                                  SiO.sub.2                                                                        (° C.)                              __________________________________________________________________________      3-1 98 2 6 54  0  0 0 20 20 1,180                                             3-2 98 2 5  5  5  5 5 25 50 1,180                                             3-3 98 2 5 10 10  5 5 35 30 1,200                                             3-4 98 2 6  0 10  0 0 34 50 1,160                                             3-5 98 2 20   5  5  5 5 30 30 1,160                                           3-6 98 2 5 15 15 10 5 20 30 1,180                                             3-7 96 4 5 15 15 10 5 20 30 1,120                                             3-8 90 10  5 15 15 10 5 20 30 1,100                                           3-9 80 20  5 15 15 10 5 20 30 1,060                                           3-10 98 2 5 10 10  5 5 35 30 1,200                                          __________________________________________________________________________    Electric properties                                                           Sample No.                                                                          Dielectric constant ε                                                             Dielectric loss tan δ (%)                                                          CR product (Ω · F)                __________________________________________________________________________      3-1 2,810 2.4 3,700                                                           3-2 2,870 2.4 3,900                                                           3-3 2,750 2.2 4,300                                                           3-4 2,620 2.3 3,200                                                           3-5 2,510 2.1 3,400                                                           3-6 2,300 2.0 3,300                                                           3-7 2,010 2.2 3,000                                                           3-8 1,780 1.9 2,600                                                           3-9 1,290 2.5 2,100                                                           3-10 1,560 5.8 1,600                                                        __________________________________________________________________________

EXAMPLE 4

Using the same dielectric powder and the same anti-reducing agents as inExample 1, multilayer ceramic capacitors were fabricated in the samemanner as in Example 1, except that a metal film formed by depositing a0.1 μm-thick copper film by vapor deposition and then forming thereon a0.9 μm-thick nickel film by electroless plating was used in place of the1.0 μm-thick vapor-deposited nickel film as the metal film deposited bya thin-film forming method and serving as the material for internalelectrodes.

Electric properties of these multilayer ceramic capacitors were measuredin the same manner as in Example 1. As a result, the properties obtainedwere substantially the same as in Example 1, in which a vapor-depositednickel film was used.

As the above Examples show, the multilayer ceramic capacitors of thepresent invention not only have a relatively high dielectric constantand a low dielectric loss, but also have a high insulation resistanceand a satisfactory CR product of 2,000 Ω·F. or higher.

In contrast, the capacitor produced without incorporation of ananti-reducing agent, i.e., Sample No. 1-10 as a comparative sample, doesnot have the properties required of capacitors. The capacitor producedusing a low temperature sintering aid in place of an anti-reducingagent, i.e., Sample No. 1-11 as a comparative sample, has an increaseddielectric loss and a reduced insulation resistance and is henceunusable as a multilayer ceramic capacitor.

The capacitor having internal electrodes formed from a paste by screenprinting without using a thin-film forming method, i.e., Sample No.2-10, has a relatively reduced dielectric constant and a relativelyincreased dielectric loss due to the oxidation of the internalelectrodes. Thus, it is understood that the thin-film forming method ispreferably used in the present invention.

The capacitor produced without conducting high-speed firing, i.e.,Sample No. 3-10, has a relatively increased dielectric loss due to someoxidation of the internal electrodes. Thus, it is understood that thehigh-speed firing is preferably used in the present invention.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A process for producing a multilayer ceramiccapacitor which comprises the steps of:forming, by a thin-film formingmethod, a nickel or nickel alloy layer on ceramic green sheetscomprising barium titanate, a bismuth oxide compound, and ananti-reducing agent; superposing said ceramic green sheets on oneanother to form an assemblage; and subjecting said assemblage tohigh-speed firing in a neutral or reducing atmosphere at a heating andcooling rate of 10° C. per minute or greater.
 2. A process for producinga multilayer ceramic capacitor as claimed in claim 1, wherein saidanti-reducing agent is represented by general formula:

    αMOx+βRO+γB.sub.2 O.sub.3 +(100-α-β-γ)SiO.sub.2

wherein MOx represents one member selected from the group consisting ofMnO₂, Li₂ O, and ZnO; R represents at least one member selected from thegroup consisting of Mg, Sr, Ca, and Ba; and α, β, and γ, each indicatingpercentage by mole, represent numbers of 5≦α≦20, 10≦β≦60, and 20≦γ≦35,respectively.
 3. A process for producing a multi-layer ceramic capacitoras claimed in claim 2, wherein the high-speed firing comprises heatingthe assemblage at an oxygen partial pressure of 10⁻⁶ to 10⁻¹⁰ MPa to atemperature in the range of 920° to 1200° C.
 4. A process for producinga multi-layer ceramic as claimed in claim 3, in which the temperature is1000-1180° C.
 5. A process for producing a multilayer ceramic capacitoras claimed in claim 1, wherein said thin-film forming method for forminga nickel or nickel alloy layer on ceramic green sheets comprises thesteps of:forming a metal layer consisting of nickel or a nickel alloy ona resin film by a thin-film forming method; patterning said metal layerinto a form of an internal electrode by photoetching; superposing saidresin film carrying said patterned metal layer on said ceramic greensheet with said metal layer being sandwiched therebetween; and pressingsaid resin film and said ceramic green sheet with heating to therebytransfer said metal layer to said ceramic green sheet.
 6. A process forproducing a multi-layer ceramic capacitor as claimed in claim 5, whereinthe high-speed firing comprises heating the assemblage at an oxygenpartial pressure of 10⁻⁶ to 10⁻¹⁰ MPa to a temperature in the range of920° to 1200° C.
 7. A process for producing a multi-layer ceramic asclaimed in claim 6 in which the temperature is 1000-1180° C.
 8. Aprocess for producing a multilayer ceramic capacitor as claimed in claim1, wherein said thin-film forming method is at least one selected fromthe group consisting of a vapor deposition method, a sputtering method,and a plating method.
 9. A process for producing a multi-layer ceramiccapacitor as claimed in claim 1, wherein the high-speed firing comprisesheating the assemblage at an oxygen partial pressure of 10⁻⁶ to 10⁻¹⁰MPa to a temperature in the range of 920° to 1200° C.
 10. A process forproducing a multi-layer ceramic as claimed in claim 9 in which thetemperature is 1000-1180° C.
 11. A process for producing a multi-layerceramic as claimed in claim 9 in which the amount of anti-reducing agentis 30 weight percent or less based on the total amount of the dielectricmaterial in an anti-reducing agent.
 12. A process for producing amultilayer ceramic as claimed in claim 11 in which the amount ofanti-reducing agent is from 1-20 weight percent based on the totalamount of the dielectric material and the anti-reducing agent.